feat: add PE image decompression and extraction pipeline (M5)

Implement full decrypt + decompress pipeline for XEX2 PE extraction:
- decompress.rs: None, Basic (zero-fill), and Normal (LZX) decompression
- extract.rs: orchestrates decryption then decompression
- Wire up CLI extract command to write PE files
- LZX decompression via lzxd crate with per-frame chunk processing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib.rs

@@ -7,8 +7,10 @@
 //! structured information from XEX2 files.
 
 pub mod crypto;
+pub mod decompress;
 pub mod display;
 pub mod error;
+pub mod extract;
 pub mod header;
 pub mod optional;
 pub mod security;